The main condition for treatment – keeping the target organs, these pharmacological concentrations of these substances, on the one hand effectively, on the other – are not toxic. To do this, you have to take into account the pharmacokinetic models – especially the distribution of the drug, the way of elimination, etc.
Given the dynamics of lidocaine concentrations in serum after a single / in the introduction. It is known that the initial rapid decrease in concentration receives a slower decrease. This feature, in two stages, most drugs.
Immediately after the introduction of almost any substance into the plasma. Once the size is relatively small, the concentration of drug in the serum is high at this stage. The material was transferred to the extravascular space. This is called the stage of marketing; Lidocaine for purposes almost completely within 30 minutes.
During the balancing phase or elimination phases occurs. At this stage, the drug concentration in the blood serum and tissue is reduced by the same rate. This dynamic feature of most drugs (in / in the introduction), although the parameters are of course different.
The drug delivery phase of an effect depending on the concentration of receptors responsible for serum. If these concentrations are approximately the same, the therapeutic effect of the drug (or lateral) will be very high – the maximum serum concentration in this step. Thus, in fast / with a low dose of lidocaine (50 mg), the antiarrhythmic effect occurs only in the initial phase of decomposition but rapidly stops (before phase equilibrium), e.g. plasma levels within therapeutics. Therefore, in order to maintain a therapeutic effect, until the equilibrium step is necessary to introduce a single high dose or low dose at short intervals.
However, a large dose carpet of toxic effects on the phase of distribution, which is not always possible. Therefore, the initial dose of phenytoin W / causes a sudden drop in pressure because the concentration is very high during the initial period. Therefore, when administered at fractional intervals to reduce the serum concentration of the appropriate (e.g., 100 mg every 3-5 min) can be used in loading / loading phenytoin. Often, when you want to insert canned / heavily loaded substances, quickly came to the receiver: A dose broken or injected slowly, but in any case – long enough time.
If the drug is administered orally, the step of distributing the concentration of serum and / or small serum (although the total amount of the substance is released into the bloodstream, in both cases the same). Indeed, after administration of a substance is absorbed relatively slowly when the blood passes substantially completely around the circumference. Therefore, the loading dose of procainamide (750 mg) (procainamide completely absorbed into the gastrointestinal tract) at once, and the pressure drop is produced, it is usually not. However, a sudden drop in blood pressure, the same dose of velocity on / in the introduction, then unfractionated (100 mg every 5 minutes) or slowly.
At the same time, substances slowly penetrate the tissue and its receptors in the concentration range (and thus the pharmacological activity), in which the serum concentration does not correspond to the distribution network. Examples of such substances are digoxin. The formulation is slowly transferred to or associated with a cellular myocardial receptor. Therefore, the distribution phase of several hours, the concentration of digoxin in the plasma decreases, but increases the concentration of the receptor and the pharmacological effect. That at the end of this step, in which a concentration of digoxin in plasma and equilibrium tissues begins to reflect a pharmacological effect. Therefore, when an appropriate dose of digoxin concentration in the serum is measured at 8.6 hours after the required administration.
When a dynamic equilibrium between drug concentrations in plasma blood concentrations and tissues, they start to decrease at the same rate (phase equilibrium). This decrease is due to the elimination of the substance and, when this step is called the elimination phase. At this stage, represents the concentration in the plasma and the concentration of the substance in the tissue.
In most cases, the elimination of first-order kinetics observed. In other words, the duration during which the plasma concentration of the drug is reduced by half (T (1/2)) does not depend (i.e., any change in the point of the concentration curve), the measurement is initiated. The concentration of the semi-logarithmic function of time in such cases, in a straight line.
If one knows, T (1/2), then at any time after administration can be calculated to the amount of material remains in the body. Decreases in the content of the substance; for example, for a time interval equal to t (1/2).
A practical withdrawal in perspective can be considered completed when the content is 90%. This means that equals terminated at time T 4/3 (1/2) (assuming that after the removal of first order kinetics).